While concrete is known for being strong, that doesn’t make it indestructible. Even concrete laid carefully can be subject to cracks, which are costly and time-consuming to repair. When the need to repair a crack does arise, it must be done with serious and careful attention to avoid further issues. We will explore the reasons these cracks happen and how to prevent them through the use of concrete form rentals, as well as the various methods of repair that can be used to save time, money, and energy while ensuring excellent results.
Why Concrete Cracks
There are a number of reasons you may see cracks in your concrete. Depending upon the root cause, the cracks may appear thinner or wider, which can help you understand the reason for the cracks. Each case should be assessed individually, but below are common reasons you may see cracks form.
Too Much Water in Mix
In order to achieve maximum strength, concrete does not require much water, but it is very common for excess water to be used in concrete on job sites. This is often done because it makes the concrete easier to install and speeds up the work, but it will ultimately reduce the strength of the concrete.
As concrete hardens and dries, the evaporation of excess mixing water can cause shrinkage. The wetter or more “soupy” the concrete mix, the more shrinkage will occur. A concrete slab can shrink as much as ½ inch per 100 feet. The force of this can pull the slab apart, creating cracks.
Too Little Water in Mix
Concrete does require some amount of water to set properly. Without this water, the slab will dry too quickly. The chemical reaction that causes concrete to go from a liquid or plastic state to a solid requires water and can take a long period of time. The right amount of water allows this reaction to occur at the correct pace and prevents cracking.
Improper Strength of Concrete
Concrete comes in a variety of different strengths, each suitable for different applications. Using the incorrect strength for your job may result in cracking.
Lack of Control Joins
A control joint helps concrete crack in controlled ways as needed. These joins should be the depth of the slab and no more than 2-3 times the thickness of the concrete. Other measurements may cause cracking that is not controlled or desirable.
Some cracks are more worrisome than others. There are four main classifications of cracks in concrete:
•Hairline cracks sit at the surface and should be repaired if they widen with time, may be a hazard, collect dirt, or are simply unsightly.
•Shrinkage cracks occur during curing and may be reduced or prevented through proper joint placement.
•Settlement cracks happen if the ground beneath the slab hasn’t been compacted properly and part of the concrete sinks.
•Structural cracks are anything wider than a credit card or that run through the entire slab and require complete replacement or extensive repair.
There is no definite answer as to what an acceptable width is for each crack. For structural cracks, the guideline of a credit card width is generally accepted, but there are other factors to consider. Some questions to ask around hairline and non-structural cracks include:
•Is the crack static or becoming wider?
•Does the crack provide a hazard, like tripping on a floor?
•Will the crack allow moisture seepage?
•Can the crack trap dirt and create a sanitation issue?
•Is the crack an eye-sore on a highly visible area?
Repairing Cracks in Concrete
If you determine a crack needs to be repaired, you will need to approach the task based on the type of crack and desired outcome. In almost all cases, the repair itself will be visible, so you must determine if that is acceptable for the project.
For thinner cracks, begin by removing any loose debris that is in the crack or the surrounding area. You can use a wire brush and broom to complete this task and ensure it is as clear as possible.
Masonry concrete crack filler is available, usually in a cartridge the size of a common caulking gun. For thin cracks, this is generally the best way to fill the crack. As an alternative, you can create a concrete patch using a vinyl concrete patching compound applied and smoothed with a putty knife. This does not require the use of a latex bonding agent.
To begin repairing a wider crack, you will need to undercut the edges of the crack using a sledgehammer and chisel. This makes it wider at the base than the surface, providing a mechanical method to key the concrete patch in place and create a secure and permanent repair. You can then clean the area in and around the crack with a wire brush and broom before washing it with water.
Mix a vinyl patching compound as directed by the manufacturer and trowel the compound into the cracks. Use a tamper to tamp the mixture and remove air pockets. You can also use a patching mortar, but be sure to mix it with a bonding agent instead of water or to coat the edges of the surface to be repaired with a bonding agent.
Once the mixture is placed, smooth the edges with a towel. When it has set based on the manufacturer’s instructions, smooth or brush the surface to match the surrounding area.
Stitching the Cracks
Another method that is used as a simple and long-lasting alternative is to use a number of holes drilled along the surface of the crack to stitch it with metallic wire. The wire is passed through these holes and anchored with grout or an epoxy-based system.
Preventing Cracks in Concrete
Ideally, you will be able to prevent cracks from forming by using proper technique when laying concrete initially. This means being sure to start with a sound subgrade and appropriately modify your concrete mix, as well as installing joints and properly curing the concrete. Doing so will save you time, money, and energy when it comes to repairs.